PhD Dissertation (Leiden University, September 7th, 2017) by Jeffrey Kotyk. This study surveys the introduction of astrology into East Asia with a primary focus on the Buddhist experience of Indian and Iranian astrology during the eighth and ninth centuries. It is argued that prior to the introduction of Esoteric Buddhism during the 8th century, the Chinese sangha had no pressing need to observe astrology. However, following the rising popularity of Tantric rituals, which require proper timing according to non-Chinese astrological conventions, Chinese Buddhism took a deep interest in astrology. This in turn prompted a wider interest in astrology among Chinese elites, encouraging the translation of more foreign works on astrology, even outside of a Buddhist context. It is shown that around the year 800 there was a shift from Indian to Iranian sources of astrology, most likely as a result of ethnic Iranians working at court. Iranian astrology, which included a rich system of horoscopy rooted in the earlier Hellenistic tradition, prompted a booming popular interest in astrology. Buddhists subsequently took up practice of horoscopy for themselves. Chinese Buddhist astrology was then exported to neighboring countries, most notably Japan where it influenced medieval religious and court cultures.